The present invention relates to a valve operating device for an internal combustion engine enabling valve timing and valve lift characteristic (valve lift and working angle or valve open period) of intake and/or exhaust valves to be varied depending upon engine operating conditions, and specifically to a variable valve timing and variable valve lift characteristic device applicable to an internal combustion engine equipped with an intake camshaft and an exhaust camshaft.
In recent years, there have been proposed and developed various variable valve timing and lift control devices each of which enables engine valve timing and valve lift characteristic of engine valves to be varied depending upon engine operating conditions, so as to reconcile improved fuel economy and enhanced combustion stability and driveability during low-speed low-load operation and enhanced intake-air charging efficiency and increased engine power during high-speed high-load operation. On such variable valve timing and lift control mechanism has been disclosed in Japanese Patent Provisional Publication No. 55-137305 (hereinafter is referred to as xe2x80x9cJP55-137305xe2x80x9d). FIG. 21 shows the variable valve timing and lift device disclosed in JP55-137305. In the device shown in FIG. 21, a camshaft 2 is provided nearby an upper middle position of the upper deck of a cylinder head 1. Camshaft 2 is integrally formed on its outer periphery with a cam 2a. A control shaft 3 whose axis is parallel to the axis of camshaft 2 is provided nearby the right-hand side of the camshaft (viewing FIG. 21). An eccentric cam 4 whose axis is eccentric to the axis of control shaft 3 is fixed to the control shaft. A rocker arm 5 is oscillatingly or rockably supported on the eccentric cam of control shaft 3. An intake valve 6 is slidably provided in cylinder head 1. A rockable cam 8 is located at the upper end of intake valve 6 through a valve lifter 7. Rockable cam 8 is oscillatingly or rockably supported by a pivot shaft 9 whose axis is laid out above valve lifter 7 in parallel with the axis of camshaft 2. The lower cam surface 8a of rockable cam 8 is in abutted-engagement with the upper surface of valve lifter 7. One end 5a of rocker arm 5 is in abutted-engagement with the cam contour surface of cam 2a, while the other end 5b of rocker arm 5 is in abutted-engagement with the upper end face 8b of rockable cam 8, so as to transmit cam action (lift) of cam 2a through rockable cam 8 and valve lifter 7 to intake valve 6, so that the intake valve is opened and closed. Control shaft 3 is rotatable within a predetermined angular range by means of an actuator (not shown). A spring 10 is provided to permanently bias the rockable cam 8 clockwise in such a manner as to force the upper end face 8b of rockable cam 8 into contact with the other end 5b of rocker arm 5. By energizing the actuator in response to a control signal from a controller (not shown), control shaft 3 is adjusted to a desired angular position based on engine operating conditions such as engine speed and load, so that the center of eccentric cam shifts and thus the center of oscillating motion of rocker arm 5 also changes. As a result, the abutted position between the other rocker-arm end 5b and the rockable-cam upper end face 8b shifts in the vertical direction (viewing FIG. 21), and thus the abutted position between the cam surface 8a of rockable cam 8 and the valve-lifter upper surface shifts. In this manner, a locus of oscillating motion of rockable cam 8 also changes, with the result that the valve timing of intake valve 6, that is, both intake-valve open timing (IVO) and intake-valve closure timing (IVC), and the valve lift of intake valve 6 can be variably controlled. Furthermore, there is a possibility of a slight change in the distance between the axis of camshaft 2 and the axis of pivot shaft 9 during operation of the engine. This may deteriorates the accuracy of variable valve timing and lift characteristic control.
It is, therefore in view of the above disadvantages, an object of the invention to provide an improved valve operating device for an internal combustion engine enabling valve timing and valve lift characteristic to be varied depending on engine operating conditions.
In order to accomplish the aforementioned and other objects of the present invention, a valve operating device for an internal combustion engine enabling both valve timing and valve lift characteristic to be varied depending on engine operating conditions comprises intake and exhaust camshafts, an eccentric cam fixedly connected to a first one of the intake and exhaust camshafts so that an axis of the eccentric cam is eccentric to an axis of the first camshaft, a rockable cam supported on the first camshaft so that the rockable cam rotates or oscillates about the axis of the first camshaft, a rocker arm oscillatingly supported on an outer periphery of the eccentric cam so that a center of an oscillating motion of the rocker arm revolves around the axis of the first camshaft, and a control shaft that variably controls the center of the oscillating motion of the rocker arm.
According to another aspect of the invention, a valve operating device for an internal combustion engine enabling both valve timing and valve lift characteristic to be varied depending on engine operating conditions comprises intake and exhaust camshafts, a rockable cam oscillatingly supported on a first one of the intake and exhaust camshafts for operating an engine valve associated with the first camshaft by an oscillating motion of the rockable cam, a drive cam fixedly connected to an outer periphery of the second camshaft adapted to be driven by an engine crankshaft for operating an engine valve associated with the second camshaft, a power-transmission mechanism that produces the oscillating motion of the rockable cam by converting a rotary motion of the second camshaft into an oscillating motion, and a control mechanism that variably controls a valve lift characteristic of the engine valve associated with the first camshaft by controlling an angular position of the first camshaft and thus changing a sliding-contact position of the rockable cam with respect to the engine valve associated with the first camshaft.
According to a still further aspect of the invention, a valve operating device for an internal combustion engine enabling both valve timing and valve lift characteristic to be varied depending on engine operating conditions comprises intake and exhaust camshafts, both adapted to be driven by an engine crankshaft, a rockable cam oscillatingly supported on a first one of the intake and exhaust camshafts for operating an engine valve associated with the first camshaft by an oscillating motion of the rockable cam, a drive cam fixedly connected to an outer periphery of the second camshaft for operating an engine valve associated with the second camshaft, a power-transmission mechanism that produces the oscillating motion of the rockable cam by converting a rotary motion of the first camshaft into an oscillating motion, and a control mechanism that variably controls a valve lift characteristic of the engine valve associated with the first camshaft by controlling an attitude of the power-transmission mechanism and thus changing a sliding-contact position of the rockable cam with respect to the engine valve associated with the first camshaft.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.